This invention relates to control arrangements for use in machining webs, such as paper machines with at least two roll pairs and/or stretch rolls, and more particularly to an improved control arrangement which permits greater speed adjustment between roll pairs and/or stretch rolls.
Various control devices are known for use in controlling the roll pairs and/or stretch rolls (hereinafter roll means) in paper machines and the like. A recent development in this area includes a control device for use in rolling mills or paper machines and has at least two roll means. With each roll means there is a drive means, e.g., a motor and an amplifier in a typical servo system for use in the speed control of its associated roll means. In addition, in some cases measuring means are disposed between adjacent roll means for measuring the condition of the paper web. The measured signal is coupled to an amplifier or adder the output of which is supplied to a multiplier along with an additional signal which is a function of the diameter of the corresponding driven roll, the gear ratio, and/or the desired tension of the paper web. The output signal of the multiplier is supplied to the corresponding amplifier. Here, in conventional fashion it is compared with an acutal speed signal developed in a tachometer generator and the driving means, e.g., the motor controlled accordingly so that the actual speed and desired speed are the same. The basic speed is established in the system and is designated V.sub.0. This basic signal is fed with some possible modification to the first driving means in the system. i.e., a drive preceding the roll means. The signal for each roll means is developed utilizing adders or summing means and the aforementioned multiplier. In this signal, the signals developed in adders associated with preceding or subsequent drive means are added to the signal for a particular drive means. For example, if for a first drive means associated with a first roll means the signal from its adder is V.sub.0 (S.sub.1) then a signal will be supplied to the adder for the second pair of rolls such it develops an output signal V.sub.0 (S.sub.1 + S.sub.2), S.sub.1 and S.sub.2 being the tensioning signals for the corresponding driving means. Similarly the output signal from the adder for the third roll means is V.sub.0 (S.sub.1 + S.sub.2 + S.sub.3).
This type of control works well with paper webs when the values of S are small. However, when such is not the case, since this is an arithmetical progression, an unreasonably high influence or subsequent driving means will occur. For example, where tensioning valves are greater than 10% problems occur. Thus, it becomes evident that there is a need for an improved type of control system of this nature.